A disc-type recording medium such as a compact disc (CD) can permanently store high-quality digital audio data, which makes such a medium popular. The “digital versatile disc” (referred as ‘DVD’ hereinafter) has been developed as a new disc-type recording medium. A DVD can store much more data than a CD, thus, more high-quality moving picture and/or audio data may be recorded on a DVD, which has enabled widespread use of the DVD. There are at least three types of DVD, DVD-ROM for read-only, DVD-R for write-once, and rewritable DVD-RAM or DVD-R/W.
Recently, another rewritable recording medium, called BD-RE (Blu-ray Disc REwritable), larger in storage capacity than a DVD has been introduced.
As shown in FIG. 1a, a rewritable disc, such as BD-RE including areas such as a clamping area 1, a transition area 2, a burst cutting area (BCA) 3, a lead-in area 4, a data zone, and a lead-out area 5.
The clamping area 1 is a center area to be clamped by a clamper of a disc device to fix the rotating disc, and the transition area 2 is an area between the clamping area 1 and the information area including the lead-in area 4 and the data zone. The BCA 3 is used to add information to the disc after completion of a disc manufacturing process. The lead-in area 4 may be where important information needed for disc reproduction is provided while the lead-out area 5 may be where a disc ending signal is provided.
The lead-in area 4 may be subdivided into several areas including a first guard area 1, a permanent information and control (PIC) area, a second guard area 2, the second information 2, OPC, a reserved area, and the first information 1.
The first guard 1 area is used as a protection area against overwriting of the PIC area by the BCA 3. The PIC area is an area where general information about the disc and various other information has been stored in a pre-recorded groove. The second guard area 2 is used as a buffering area for the changeover from the pre-recorded area to the rewritable area, and the first and the second information areas are used to store specific information about the disc or applications, such as control information.
FIGS. 1b and 1c show an exemplary RUB (Recording Unit Block). A single RUB, which corresponds to a single ECC (Error Correction Code) block, is composed of Run-in, physical cluster, Run-out, and guard areas, as shown in FIG. 1b. If more than one RUB, for example, successive RUBs, are created at one time to store real-time input data, e.g., A/V data, the set of Run-in, physical and Run-out is repeated as many times as necessary and a guard area ‘Guard_3’ is formed at the end, as shown in FIG. 1c. 
The Run-in area, as shown in FIG. 2a, may include a 1100-channel-bit guard ‘Guard_1’ and a 1660-channel-bit preamble ‘PrA’. 55 repetitions of a 20-channel-bit pattern are written in the guard ‘Guard_1’ to indicate the head of an RUB while the first sync data ‘Sync_1’ and the second sync data ‘Sync_2’, which are 30 channel bits in length, are written in the preamble ‘PrA’. Each sync data is composed of 24-bit sync body and 6-bit sync ID. The sync IDs of the first and the second sync data are ‘000 100’(FS4) and ‘010 000’(FS6), respectively.
The Run-out, as shown in FIG. 2b, is composed of a 540-channel-bit guard ‘Guard—2’ and a 564-channel-bit post-amble ‘PoA’ including the third sync data ‘Sync_3’. The third sync data also includes a 24-bit sync body and 6-bit sync ID. The third sync ID is ‘000 001’(FS0).
The guard ‘Guard—2’ is created to prevent overlap between previously-recorded data and new data to be recorded and may have 27 repetitions of a 20-channel-bit pattern to indicate the end of a previously-recorded area, namely, a just-recorded RUB.
User data is written in the physical cluster and the user data is restored to original data by a signal processor that uses a clock synchronized with sync data written in the Run-in.
FIG. 1d shows recording format of a physical cluster of a BD-RE where 31 recording frames (frames #0˜#30) are recorded. The mutually-different 7 frame syncs used for BD-RE (FSs #0 to #6) may be written in the 31 recording frames in a unique order, as shown in FIG. 1d. 
FIG. 1e shows the types and patterns of frame syncs to be written in a physical cluster. As shown in FIG. 1e, a total 7 frame syncs are used and each frame sync is composed of 24-bit sync body and 6-bit sync identifying pattern which is different among the 7 frame syncs.
Each RUB, which corresponding to a single ECC block, has physical address information, e.g., an address unit number (AUN) to enable random access of an arbitrary RUB written on a BD-RE. The physical address information is written in a physical cluster of an RUB after modulated and encoded along with audio/video (A/V) data. An AUN is derived from physical sector number (PSN) that has not been actually written on a BD-RE.
In the case of a write-once or a rewritable disc (DVD-R, -RW, -RAM, +R, +RW), a linking frame is created behind a previously-recorded area before new data is recorded discontinuous with the previously-recorded data. However, a read-only disc, such as DVD-ROM and video CD, does not need a linking frame to link two data sections because it contains completely-recorded data.
Such a difference between a writable and a read-only disc requires an ordinary disc player, such as a DVD-player or a DVD-ROM drive, to be equipped with additional hardware and/or software to play back both types of discs.
A disc device capable of recording/reproducing a writable disc should also be equipped with additional hardware and/or software to play back a read-only disc as well as a writable disc.
The standard of a high-density read-only recording medium, called ‘BD-ROM’, is also under discussion together with the standardization of a BD-RE. If the physical format of a BD-ROM was the same as BD-RE, a disc player would be able to apply the same reproduction algorithm to both recording media. In addition, both types of disks should be distinguishable, as well as, have compatible formats. A suitable solution to harmonize these contrary conditions has not yet been provided.